Vegas renders really slowly?

Hi, I am having a bit of a frustration with vegas. I have a project that is 1920x1080. I can play a "Best - Full" at 23.976 FPS but rendering that to a mp4 or mov file only seems to encode at 2fps??? Now i have never had this before, and i have not changed by pc setup, not installed more programs, and dont have any viruses. I dont understand? What can i do to make it encode faster???